Brush seal for static turbine components

ABSTRACT

A brush seal is provided between static components of a turbine. The turbine flowpath has an inlet spaced from another the inner web of the first stage nozzle. A brush seal is disposed between the two static components to minimize leakage flow to the packing casing region. The bristles of the brush seal are preloaded to fill any gap between the static components caused by distortion or out-of-roundness of the opposed surfaces being sealed. A side plate may contact the opposed sealing surface, increasing the pressure capability of the brush seal and minimizing overall seal leakage by providing the minimum possible flow area restricted solely by the bristles.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a brush seal for sealing betweenstatic components of a turbine and particularly relates to a brush sealfor sealing between an inlet and the inner web of a first stage nozzleto minimize leakage flows into the inlet packing ring region of a steamturbine.

[0002] Seals are oftentimes employed between static components of aturbine. For example, in a steam turbine, static seals are employed inthe inlet region to minimize steam leakage flows into packing ringlocations between the packing ring casing and the rotor and forming thehigh pressure end seals. The seals, for example, between the inlet andthe inner web of the first stage nozzle have included a plurality oflabyrinth seal teeth mounted on sealing ring segments which may bespring biased to engage and seal against the opposing component. Thepacking ring seals carrying the labyrinth teeth can be preloaded andoriented in either radially outward or radially inward directions,depending on which component of the inlet region the seals are mounted.While labyrinth seals have been effective for minimizing leakage flowsin these high pressure regions, the static annular or cylindricalcomponents may become out-of-round or distorted which can result inincreased leakage flow from the high pressure region to the highpressure end seal packing ring region. Thermal distortion or creep ofone or both of the components can cause an out-of-roundness and thecreation of a gap between the tips of the labyrinth seal teeth and thesurface that they are sealing against. Thus, as long as the labyrinthseal teeth and the component parts remain circular, the labyrinth teethare effective to minimize leakage flows. However, if one or both of thesealing surfaces becomes out-of-round, a generally crescent-shaped gapis created between the tips of the teeth and the adjacent sealingsurface, resulting in leakage across the seal through the gap and aperformance loss. Any increased leakage past the labyrinth seal teethdecreases the effectiveness of the energetic fluid, e.g., steam, flowingalong the flowpath of the turbine. Consequently, there is a need for asealing arrangement between static components of a turbine which willaccommodate distortion or out-of-roundness of the components to besealed while maintaining an effective seal.

[0003] In a preferred embodiment according to the present invention,there is provided a static seal for a turbine, comprising first andsecond stationary turbine components having respective first and secondsurfaces in opposition to one another, at least one of the firstcomponents being subject to distortion, opening a gap between the firstsurface and the second surface and a brush seal carried by one of thefirst and second components having a plurality of bristles with aninitial interference between tips of the bristles and another of thefirst and second components for compliant engagement with another of thefirst and second components maintaining the seal between the surfacesand across the gap.

[0004] In a further preferred embodiment according to the presentinvention, there is provided a steam path including a steam inlet and afirst stage nozzle having an inner web, the inlet and inner web havingrespective first and second surfaces in generally radial opposition toone another, at least one of the inlet and the inner web being subjectto distortion opening a gap between the first surface and said secondsurface and a brush seal carried by one of the inlet and the inner webhaving a plurality of bristles with an initial interference between tipsof the bristles and another of the inlet and the inner web for compliantengagement with another of the inlet and the inner web maintaining astatic seal between the surfaces and across the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a fragmentary cross-sectional view illustrating aflowpath for the first stage of a turbine including conventional sealsbetween the turbine inlet and inner web of the first stage nozzleaccording to the prior art;

[0006]FIG. 2 is a view similar to FIG. 1 illustrating a different formof prior art seal;

[0007]FIG. 3 is a fragmentary cross-sectional view of the inlet regionof a turbine illustrating a static seal according to a preferredembodiment of the present invention;

[0008]FIG. 4 is a view similar to FIG. 3 illustrating a further form ofstatic seal hereof; and

[0009]FIG. 5 is an enlarged fragmentary cross-sectional view of thestatic seal illustrated in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Referring now to the drawings, particularly to FIG. 1, there isillustrated a rotary component of a turbine, generally designated 10,including a rotor having a rotor wheel 12 mounting a plurality ofcircumferentially spaced buckets 14 and rotatable about an axis. Astationary component of the turbine includes a nozzle 16 formed of aplurality of circumferentially spaced airfoils extending between innerand outer bands 18 and 20, respectively, and carrying an inner web 22.Fluid, for example, steam, is provided an inlet region 26 for flowthrough the nozzle 16 and buckets 14, which form a portion of theflowpath indicated by the arrow 28 through the turbine. Inlet region 26includes an inlet 29 adjacent the inner web 22, the inlet 29 having anouter surface 30 in part defining the fluid flowpath 28 into the firststage of the turbine defined by the nozzles 16 and buckets 14. The inlet29 and inner web 22 are typically sealed one to the other by a pluralityof annular packing ring segments 34 carrying a plurality of labyrinthseal teeth 36. Packing ring segments 34 are generally spring biased suchthat the labyrinth teeth 36 lie in close proximity to the opposedsealing surface of inlet 29. In this conventional configuration, theseal ring segments 34 have labyrinth teeth 36 directed generally in aradially outward direction.

[0011] Referring to FIG. 2, which illustrates a further form of priorart seal between an inlet 29 for a turbine and an inner web 22, the sealbetween the inlet 29 and inner web 22 includes a plurality ofcircumferentially spaced packing ring segments 38 mounting labyrinthseal teeth 40 for minimizing leakage flow into the packing ring region,generally designated 44. As illustrated in FIGS. 1 and 2, the packingring segments 34 and 38 can be directed radially outwardly or inwardly,respectively. The packing ring segments and inlet or inner web member,as applicable, form a static seal between the inlet and inner web. Asindicated previously, distortion of one or both of these components,however, may cause the component(s) to become out-of-round, creating agap, for example, a crescent-shaped gap, between the out-of-roundcomponents. Any such gap causes increased leakage past the labyrinthseal teeth and a consequent turbine performance loss.

[0012] In accordance with a preferred embodiment of the presentinvention as illustrated in FIG. 3, there is provided a brush seal forsealing between static components of a turbine. The turbine, generallydesignated 49, includes a nozzle 50 including a plurality of airfoils 52circumferentially spaced one from the other between inner and outerbands 54 and 56 and carrying an inner web 58. The rotor includes a rotorwheel 60 mounting a plurality of buckets 62. In the inlet region 64 ofthe turbine flowpath indicated 66, a static seal, generally indicated63, is disposed between the inlet 68 and a flange 70 of the inner web58. The seal 63 is preferably comprised of a plurality of arcuatepacking ring segments 72 each mounting a brush seal 74. The brush sealcomprises a plurality of bristles 75 which may be formed of metal ornon-metallic materials, such as ceramics, carbon fiber or silica,disposed between a pair of side plates 76 on opposite axial sides ofbristles 75. The side plates and bristles are preferably secured to oneanother by welding, for example, as illustrated at 78, although it willbe appreciated that other modalities of securement may be used such ascrimping, high temperature glues or adhesive. Brush seal 74 is formed ina groove of the packing ring segment which may also include one or morelabyrinth seal teeth 80 in combination with the brush seal 74.Preferably, the bristles 75 of the brush seal are assembled with aninterference to the adjacent sealing surface, e.g., the inlet 68. Thatis, a preload is provided on the bristles to fill any radial gap betweenthe static components being sealed, i.e., the inlet and inner web, inthe event that one or more of the components becomes out-of-round due todistortion or creep. The preload on the bristles causes the tips of thebristles to fill any such gap. In FIG. 3, the packing ring segments 72are preferably biased in a radial outward direction, maintaining thetips of the bristles in engagement with the inlet 68.

[0013] Referring now to FIG. 4 illustrating a further embodiment of thepresent invention, there is illustrated a pair of stationary components81 and 82 forming a leakage path 84 for fluid, e.g., steam, to alocation between packing rings 86 and 88 forming part of the packingring end seal region. Packing rings 86 and 88 form seals with theturbine rotor 90 at the high pressure end of the turbine. Between thestatic components 81 and 82, there are provided a plurality of arcuatepacking ring segments 92 which are preferably spring biased in a radialinward direction. Each packing ring segment 92 mounts a brush seal 174including side plates 176 which straddle bristles 175. The tips of thebristles 175 project from the packing ring segments for engagement witha surface on the static component 81 forming a seal between staticcomponents 81 and 82. The packing ring segments 92 may also include oneor more labyrinth seal teeth 180 forming a combination brush/labyrinthseal. As in the previous embodiment, the bristles 175 are preloaded,enabling the tips of the bristles to continuously engage the surface ofthe opposing static component 81. By preloading the bristles 175, it isalso possible to locate the backing plate supporting the bristles incontact with the adjacent sealing surface. By providing thismetal-to-metal contact, the pressure capability of the brush seal isincreased and overall seal leakage is minimized, i.e., the minimumpossible flow area restricted solely by the bristle pack is minimized.

[0014] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A static seal for a turbine, comprising: firstand second stationary turbine components having respective first andsecond surfaces in opposition to one another, at least one of said firstcomponents being subject to distortion, opening a gap between said firstsurface and said second surface; and a brush seal carried by one of saidfirst and second components having a plurality of bristles with aninitial interference between tips of the bristles and another of saidfirst and second components for compliant engagement with said anotherof the first and second components maintaining the seal between thesurfaces and across the gap.
 2. A seal according to claim 1 wherein saidsurfaces are generally cylindrical and concentric relative to oneanother about an axis of the turbine, said bristles extending generallyin a radial direction.
 3. A seal according to claim 2 wherein saidbristles project in a generally radially outward direction.
 4. A sealaccording to claim 2 wherein said bristles project in a generallyradially inward direction.
 5. A seal according to claim 1 wherein saidone component carries at least one labyrinth seal tooth.
 6. A sealaccording to claim 1 wherein said bristles are biased for movement ofsaid bristle tips toward said another of said first and secondcomponents upon the opening of the gap between said surfaces to fill thegap with said bristle tips.
 7. A seal according to claim 1 wherein saidbrush seal includes at least one side plate on one side of the bristlesand carried by and extending from said one component toward another ofsaid first and second components.
 8. A seal according to claim 7 whereinsaid one side plate lies in contact with said another of said first andsecond components.
 9. A steam path including a steam inlet and a firststage nozzle having an inner web; said inlet and inner web havingrespective first and second surfaces in generally radial opposition toone another, at least one of said inlet and said inner web being subjectto distortion opening a gap between said first surface and said secondsurface; and a brush seal carried by one of said inlet and said innerweb having a plurality of bristles with an initial interference betweentips of the bristles and another of said inlet and said inner web forcompliant engagement with said another of said inlet and said inner webmaintaining a static seal between the surfaces and across the gap.
 10. Aturbine according to claim 9 wherein said surfaces are generallycylindrical and concentric relative to one another about an axis of theturbine, said bristles extending generally in a radial direction.
 11. Aturbine according to claim 10 wherein said bristles are carried by saidinner web and project in a generally radially outward direction with thebristle tips in engagement with said inlet.
 12. A turbine according toclaim 10 wherein said bristles are carried by said inlet and project ina generally radially inward direction with said bristle tips inengagement with said inner web.
 13. A turbine according to claim 9wherein said one of said inlet and said inner web carries at least onelabyrinth seal tooth.
 14. A turbine according to claim 9 wherein saidbristles are biased for movement of said bristle tips toward saidanother of said inlet and said inner web upon the opening of the gapbetween said surfaces to fill the gap with said bristle tips.
 15. Aturbine according to claim 9 wherein said brush seal includes at leastone side plate on one side of the bristles and carried by and extendingfrom said one of said inlet and said inner web toward said another ofsaid inlet and said inner web.
 16. A turbine according to claim 15wherein said one side plate lies in contact with said another of saidinlet and said inner web.